1. Field of the Invention
The present invention relates to an endoscope apparatus, more particularly, a constitution used in medical fields for forming and displaying a spectral image (video) made up of image information of arbitrarily selected wavelength ranges.
2. Description of the Related Art
Recently, in a electronic endoscope apparatus which uses a solid imaging device, spectral imaging combined with a narrow bandpass filter on the basis of a spectral reflectance in alimentary canal (gastric mucosa and the like), namely, a narrow band filter built-in an electronic endoscope apparatus (Narrow Band Imaging-NBI) has become the focus of attention. In place of rotational filters of R (red), G (green) and B (blue) by a frame sequential method, this system is provided with band pass filters of three narrow bands (wavelengths), outputs sequentially illumination light via these narrow bandpass filters, and conducts processing the same as in the case of red (R), green (G) and blue (B) signals while changing respective weightings to three signals obtained from these illumination lights, thereby forming a spectral image. This spectral image is able to realize micro-structures and the like in gastrointestinal tracts such as the stomach and large-intestine, which would otherwise not be realized.
In contrast, unlike the frame sequential method using the above-described narrow bandpass filters, as described in Japanese Published Unexamined Patent Application No. 2003-93336, it has been proposed that in the simultaneous method in which micro-mosaic color filters are arranged on a solid imaging device, a spectral image is formed by the computing process on the basis of image signals obtained from white light. In this method, the relationship between numeric data of the respective R, G, and B color sensitivity characteristics and numeric data of spectral characteristics of a specific narrow bandpass is determined as matrix data (coefficient sets) and computing is made for the matrix data and the R, G and B signals to obtain spectral image signals artificially via the narrow band pass filters. Where a spectral image is formed by such computing, it is not necessary to provide a plurality of filters corresponding to desired wavelength ranges and to provide these change-over arrangements, thereby successfully avoiding increases in the size of a system and reducing cost.
However, endoscope apparatuses in which different types of endoscopes (scope) are connected to a single processor unit have been recently used, and user-friendly endoscope apparatuses have been demanded in view of such circumstances.
Further, in the computing processing of spectral images in the endoscope apparatus, such a problem has been brought about that underlying RGB color image signals are different depending on types of color filters of an imaging device (solid imaging device and others), spectral sensitivity characteristics, types of light sources and spectral sensitivity characteristics of optical system components of an endoscope such as a light guide, and the constitutions of a endoscope or light source influence formation of a spectral image, resulting in a difference in reproducibility in the same wavelength range. More specifically, a CCD, and a solid imaging device, includes a complementary color-type CCD having color filters of Mg, Ye, Cy and G and an elementary color-type CCD having RGB color filters, different in spectral sensitivity characteristics according to individual differences. FIG. 5 shows an example of spectral sensitivity characteristics of color filters of a complementary color type CCD. The color filters Mg, Ye, Cy and G, differ in spectral sensitivity according to individual differences in CCD. In the computing processing employing single matrix data, such difference in spectral characteristics is reflected in the computing result, thereby influencing formation of a spectral image.